Ethylene polymer composition and use thereof in polyolefin composition

ABSTRACT

Ethylene polymer composition having a fusion enthalpy ΔH fus , measured by Differential Scanning calorimetry with a heating rate of 20° C. per minute, of 60 J/g or more, comprising, all per cent amounts being by weight:
         A) 25-55% of an ethylene polymer containing 10% or less, referred to the weight of A), of a fraction XS A  soluble in xylene at 25° C.;   B) 45-75% of a copolymer of ethylene and propylene containing from 45% to 70%, of ethylene and 60% or more of a fraction XS B  soluble in xylene at 25° C., both the ethylene of the copolymer and XS B  amounts being referred to the weight of B);
 
wherein the amounts of A) and B) are referred to the total weight of A)+B).

FIELD OF THE INVENTION

The present disclosure relates to an ethylene polymer composition and toits use as an additive, in particular as an impact modifier, forpolyolefin compositions.

BACKGROUND OF THE INVENTION

Impact modifiers, consisting of or comprising a prevailingly amorphousolefin copolymer, may be added in polyolefin compositions to enhance theimpact resistance and optionally optical properties.

Applicants presently believe that by properly balancing the total fusionenthalpy with the hydrocarbon-solubility of specific polymer components,it is possible to obtain an ethylene polymer composition particularlysuited for preparing final polyolefin compositions having a particularset of properties.

In particular, the ethylene polymer composition of the presentdisclosure provides polyolefin compositions having a balance of impactresistance at low temperatures, optical properties (high gloss) andreduced shrinkage on cooling.

SUMMARY OF THE INVENTION

The present disclosure provides ethylene polymer compositions having afusion enthalpy ΔH_(fus), measured by Differential Scanning calorimetrywith a heating rate of 20° C. per minute or more, of 60 J/g or more,preferably of 70 J/g or more, and comprising, all percent amounts beingby weight:

-   -   A) 25-55%, alternatively 30-45%, of an ethylene polymer        containing 10% or less, alternatively 8% or less, alternatively        5% or less, referred to the weight of A), of a fraction XS_(A)        soluble in xylene at 25° C.;    -   B) 45-75%, alternatively 55-70%, of a copolymer of ethylene and        propylene containing from 45% to 70%, alternatively from 50% to        70%, of ethylene and 60% or more, alternatively 65% or more, in        particular 70% or more, of a fraction XS_(B) soluble in xylene        at 25° C., both the ethylene of the copolymer and XS_(B) amounts        being referred to the weight of B);        wherein the amounts of A) and B) are referred to the total        weight of A)+B).

DETAILED DESCRIPTION OF THE INVENTION

In general, the term “copolymer” is meant to include also polymerscontaining more than one kind of comonomers, such as terpolymers.

The upper limit of ΔH_(fus) for the ethylene polymer composition of thepresent disclosure may be 90 J/g. This upper limit applies to the lowerlimits specified in the present disclosure.

The ethylene polymer A) may be an ethylene homopolymer (i) or acopolymer (ii) of ethylene with one or more comonomers selected fromolefins having formula CH₂═CHR wherein R is an alkyl radical, linear orbranched, having from 1 to 10 carbon atoms, or a mixture of (i) and(ii).

Specific examples of said olefins are propylene, butene-1, pentene-1,4-methylpentene-1, hexene-1, octene-1 and decene-1.

The ethylene polymer A) may have a density of from 0.930 to 0.960 g/cm³,more alternatively from 0.935 to 0.955 g/cm³, alternatively from 0.940to 0.955 g/cm³, determined according to ISO 1183 at 23° C.

The component B) in the ethylene polymer composition of the presentdisclosure may be an ethylene copolymer which is optionally more solublein xylene, thus less crystalline, than component A).

The upper limit of XS_(B) content in component B) may be 90% by weight.This upper limit applies to all the lower limits specified above.

The intrinsic viscosity [η] of the XS_(B) fraction may be of 2 dl/g ormore, alternatively from 2 to 3.5 dl/g.

The ethylene polymer composition of the present disclosure may have amelting peak at a temperature Tm of 120° C. or higher, alternativelyfrom 120° C. to 130° C., measured by Differential Scanning calorimetrywith a heating rate of 20° C. per minute.

The melt flow rate (MFR) of the ethylene polymer composition may be from0.3 to 5 g/10 min., alternatively from 0.5 to 3 g/10 min., determinedaccording to ISO 1133 at 230° C. with a load of 2.16 kg.

Moreover, the ethylene polymer composition of the present disclosure mayhave at least one of the following additional features:

-   -   a MFR value of the ethylene polymer A), determined according to        ISO 1133 at 230° C. with a load of 2.16 kg, of from 1 to 15 g/10        min.;    -   a glass transition temperature (Tg), measured on the blend of        A)+B), of equal to or higher than −50° C., alternatively from        −35 to −50° C.;    -   Tg of component B) of equal to or higher than −50° C.,        alternatively from −35 to −50° C.;    -   an ethylene content, determined on the total amount of A)+B), of        65%-85% by weight, alternatively of 65-80% by weight;    -   an amount of total fraction XS_(TOT) soluble in xylene at 25°        C., determined by extraction carried out on the total amount of        A)+B), of 35%-60% by weight, alternatively of 40-60% by weight;    -   an intrinsic viscosity [η] of the XS_(TOT) fraction of 1.8 dl/g        or more, alternatively from 1.8 to 3.0 dl/g;    -   an ethylene content of the the XS_(TOT) fraction of 45%-60% by        weight;    -   a flexural modulus value from 90 to 200 MPa.

All the said [η] values are measured in tetrahydronaphthalene at 135° C.

Applicants presently believe that in the composition of the presentdisclosure, the Tg of B) may substantially determine the Tg of the blendof A)+B), so that, when the Tg value measured on the blend of A)+B) isof −48° C. or higher, the Tg of B) has still to be equal to or higherthan −50° C.

While there is no limitation in principle on the kind of polymerizationprocess and catalysts to be used, it has been found that the ethylenepolymer composition of the present disclosure can be prepared bysequential polymerization. The sequential polymerization may comprise atleast two sequential steps. In such a two sequential step process,components A) and B) may be prepared in separate subsequent steps,operating in each step, except the first step, in the presence of thepolymer formed and the catalyst used in the preceding step. The catalystmay be added only in the first step, however its activity is such thatit may still be active for all subsequent steps.

The polymerization, which can be continuous or batch, may be carried outoperating in liquid phase, in the presence or not of inert diluent, orin gas phase, or by mixed liquid-gas techniques.

Reaction time, pressure and temperature relative to the polymerizationsteps may not be critical, however in various embodiments thetemperature is in a range of from 50 to 100° C. The pressure may beatmospheric or higher.

The regulation of the molecular weight may be carried out by usingregulators such as hydrogen.

The polymerizations of the present disclosure may be carried out in thepresence of a Ziegler-Natta catalyst. Typically a Ziegler-Natta catalystcomprises the product of the reaction of an organometallic compound ofgroup 1, 2 or 13 of the Periodic Table of elements with a transitionmetal compound of groups 4 to 10 of the Periodic Table of Elements (newnotation). In particular, the transition metal compound may be selectedamong compounds of Ti, V, Zr, Cr and Hf and is preferably supported onMgCl₂.

In various embodiments, the catalysts may comprise the product of thereaction of the organometallic compound of group 1, 2 or 13 of thePeriodic Table of elements, with a solid catalyst component comprising aTi compound and an electron donor compound supported on MgCl₂.

In an embodiment, the organometallic compounds may be aluminum alkylcompounds.

In a particular embodiment, the ethylene polymer composition of thepresent invention may be obtainable by using a Ziegler-Nattapolymerization catalyst, alternatively a Ziegler-Natta catalystsupported on MgCl₂, alternatively a Ziegler-Natta catalyst comprisingthe product of reaction of:

-   1) a solid catalyst component comprising a Ti compound and an    electron donor (internal electron-donor) supported on MgCl₂;-   2) an aluminum alkyl compound (cocatalyst); and, optionally,-   3) an electron-donor compound (external electron-donor).

The solid catalyst component (1) may contain as an electron-donor acompound generally selected among the ethers, ketones, lactones,compounds containing N, P and/or S atoms, and mono- and dicarboxylicacid esters.

Embodiments of catalysts having the above mentioned characteristics aredescribed in U.S. Pat. No. 4,399,054 and European Patent No. 45977.

In various embodiments, the electron-donor compounds may be phthalicacid esters, alternatively diisobutyl phthalate, and succinic acidesters.

Suitable succinic acid esters may be represented by the formula (I):

wherein the radicals R₁ and R₂, equal to or different from each other,are a C₁-C₂₀ linear or branched alkyl, alkenyl, cycloalkyl, aryl,arylalkyl or alkylaryl group, optionally containing heteroatoms; theradicals R₃ to R₆ equal to or different from each other, are hydrogen ora C₁-C₂₀ linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkylor alkylaryl group, optionally containing heteroatoms, and the radicalsR₃ to R₆ which are joined to the same carbon atom can be linked togetherto form a cycle.

R₁ and R₂ may be C₁-C₈ alkyl, cycloalkyl, aryl, arylalkyl and alkylarylgroups. In various embodiments, R₁ and R₂ may be selected from primaryalkyls and in particular branched primary alkyls. Examples of suitableR₁ and R₂ groups may include methyl, ethyl, n-propyl, n-butyl, isobutyl,neopentyl, 2-ethylhexyl.

In various embodiments, the compounds described by the formula (I) maybe that in which R₃ to R₅ are hydrogen and R₆ is a branched alkyl,cycloalkyl, aryl, arylalkyl and alkylaryl radical having from 3 to 10carbon atoms. Alternatively, the group of compounds within those offormula (I) may be those in which at least two radicals from R₃ to R₆are different from hydrogen and are selected from C₁-C₂₀ linear orbranched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl group,optionally containing heteroatoms. In various embodiments, the tworadicals R₃ to R₆ may be different from hydrogen and are linked to thesame carbon atom. In still further embodiments, the compounds in whichat least two radicals different from hydrogen are linked to differentcarbon atoms, that is R₃ and R₅ or R₄ and R₆ may be used.

Other electron-donors particularly suited may be the 1,3-diethers, asillustrated in published European patent applications EP-A-361 493 and728769.

As cocatalysts (2), one may use the trialkyl aluminum compounds, such asAl-triethyl, Al-triisobutyl and Al-tri-n-butyl.

The electron-donor compounds (3) that may be used as externalelectron-donors (added to the Al-alkyl compound) include the aromaticacid esters (such as alkylic benzoates), heterocyclic compounds (such asthe 2,2,6,6-tetramethylpiperidine and the 2,6-diisopropylpiperidine),and silicon compounds containing at least one Si-OR bond (where R is ahydrocarbon radical).

Examples of the said silicon compounds are those of formula R¹ _(a)R²_(b)Si(OR³)_(c), where a and b are integer numbers from 0 to 2, c is aninteger from 1 to 3 and the sum (a+b+c) is 4; R¹, R² and R³ are alkyl,cycloalkyl or aryl radicals with 1-18 carbon atoms optionally containingheteroatoms.

Useful examples of silicon compounds include (tert-butyl)₂Si(OCH₃)₂,(cyclohexyl)(methyl)Si (OCH₃)₂, (phenyl)₂Si(OCH₃)₂ and(cyclopentyl)₂Si(OCH₃)₂.

The previously said 1,3-diethers are also suitable to be used asexternal donors. In various embodiments, the case that the internaldonor is one of the said 1,3-diethers, the external donor can beomitted.

The catalysts may be precontacted with small quantities of olefin(prepolymerization), maintaining the catalyst in suspension in ahydrocarbon solvent, and polymerizing at temperatures from room to 60°C., thus producing a quantity of polymer from 0.5 to 3 times the weightof the catalyst.

The catalyst may alternatively be precontacted with liquid monomer,producing a quantity of polymer up to 1000 times the weight of thecatalyst.

The ethylene polymer composition of the present disclosure can alsocontain additives, such as without limitation antioxidants, lightstabilizers, heat stabilizers, colorants and fillers.

As previously said, the ethylene polymer composition of the presentdisclosure may be compounded with additional polyolefins, in particularpropylene polymers such as propylene homopolymers, random copolymers,and thermoplastic elastomeric polyolefin compositions. Accordingly, inan alternative embodiment of the present disclosure, a polyolefincomposition may contain the above-defined ethylene polymer composition.In various embodiments, the polyolefin composition may comprise at least50% by weight, alternatively from 50% to 85% by weight, of one or moreadditional polyolefins, thus 50% or less, alternatively from 15% to 50%by weight, of the ethylene polymer composition according to the presentdisclosure, all percent amounts being referred to the total weight ofthe ethylene polymer composition and of the additional polyolefin orpolyolefins.

Alternative examples of the said additional polyolefins may include thefollowing polymers:

-   1) crystalline propylene homopolymers, such as isotactic or mainly    isotactic homopolymers;-   2) crystalline propylene copolymers with ethylene and/or a C₄-C₁₀    α-olefin, wherein the total comonomer content ranges from 0.05 to    20% by weight with respect to the weight of the copolymer, and    wherein the C₄-C₁₀ α-olefins may include without limitation    1-butene; 1-hexene; 4-methyl-1-pentene and 1-octene;-   3) crystalline ethylene homopolymers and copolymers with propylene    and/or a C₄-C₁₀ α-olefin, such as high density polyethylene    (“HDPE”);-   4) thermoplastic elastomeric compositions comprising one or more of    propylene homopolymers and/or the copolymers of item 2) and an    elastomeric moiety comprising one or more copolymers of ethylene    with propylene and/or C₄-C₁₀ α-olefins, optionally containing minor    quantities of a diene, such as butadiene, 1,4-hexadiene,    1,5-hexadiene and ethylidene-1-norbornene, wherein the diene content    may be from 1 to 10% by weight, optionally prepared by mixing the    components in the molten state or by sequential polymerization, and    optionally containing the said elastomeric moiety in quantities from    5 to 80% by weight.

The polyolefin composition may be manufactured by mixing the ethylenepolymer composition and the additional polyolefin(s) together, extrudingthe mixture, and pelletizing the resulting composition using knowntechniques and apparatus.

The polyolefin composition may also contain conventional additives,including without limitation mineral fillers, colorants and stabilizers.Mineral fillers that can be included in the composition include talc,CaCO₃, silica, such as wollastonite (CaSiO₃), clays, diatomaceaousearth, titanium oxide and zeolites. The mineral filler may be inparticle form having an average diameter ranging from 0.1 to 5micrometers.

The present disclosure also provides final articles, in particularinjection molded articles, such as finished parts for the automotiveindustry (such as bumpers and fascia), made of or comprising the saidpolyolefin composition.

Analytical Methods

The following analytical methods may be used to characterize the polymercompositions.

Melting temperature (ISO 11357-3)

Determined by differential scanning calorimetry (DSC). A sampleweighting 6±1 mg was heated to 200±1° C. at a rate of 20° C./min andkept at 200 ±1° C. for 2 minutes in nitrogen stream and was thereaftercooled at a rate of 20° C./min to 40±2° C., thereby kept at thistemperature for 2 min to crystallize the sample. Then, the sample wasagain melted at a temperature rise rate of 20° C./min up to 200° C.±1.The melting scan was recorded, a thermogram was obtained, and, fromthis, temperatures corresponding to peaks were read. The temperaturecorresponding to the most intense melting peak recorded during thesecond fusion was taken as the melting temperature. The fusion enthalpyΔH_(fus) was measured on said most intense melting peak. If only onepeak was detected, both melting temperature and ΔH_(fus) were providedby (i.e. measured on) such peak. To determine fusion enthalpy ΔH_(fus),the base-line was constructed by connecting the two closest points atwhich the melting endotherm peak deviate from the baseline. The heat offusion (ΔH_(fus)) was then calculated by integrating the area betweenDSC heat flow recorded signal and constructed baseline.

Xylene Soluble Fraction

2.5 g of polymer and 250 cm³ of o-xylene were introduced in a glassflask equipped with a refrigerator and a magnetic stirrer. Thetemperature was raised over 30 minutes from room temperature up to theboiling point of the solvent (135° C.). The so obtained clear solutionwas then kept under reflux and stirring for a further 30 minutes. Theclosed flask was then kept in a thermostatic water bath at 25° C. for 30minutes as well so that the crystallization of the insoluble (XI) partof the sample takes place. The so formed solid was filtered on quickfiltering paper. 100 cm³ of the filtered liquid was poured in apreviously weighed aluminum container which is heated on a heating plateunder nitrogen flow, to remove the solvent by evaporation. The containerwas then kept in an oven at 80° C. under vacuum to dryness and thenweighed after constant weight was obtained.

Thus one calculated the percent by weight of polymer soluble andinsoluble in xylene at 25° C.

Melt Flow Rate

The melt flow rate was measured according to ISO 1133 at 230° C. with aload of 2.16 kg, unless otherwise specified.

[η] intrinsic viscosity

The sample was dissolved in tetrahydronaphthalene at 135° C. and thenwas poured into the capillary viscometer. The viscometer tube (Ubbelohdetype) was surrounded by a cylindrical glass jacket; this setup allowstemperature control with a circulating thermostated liquid. The downwardpassage of the meniscus was timed by a photoelectric device.

The passage of the meniscus in front of the upper lamp starts thecounter which had a quartz crystal oscillator. The meniscus stops thecounter as it passes the lower lamp and the efflux time was registered:this was converted into a value of intrinsic viscosity through Huggins'equation (Huggins, M. L., J. Am. Chem. Soc., 1942, 64, 2716) providedthat the flow time of the pure solvent was known at the sameexperimental conditions (same viscometer and same temperature). Onesingle polymer solution was used to determine [η].

Ethylene or Propylene content determined via I.R. Spectroscopy

The NIR (6000-5500 cm⁻¹) spectrum of as pressed film of the polymer wasrecorded in absorbance vs. wavenumbers (cm⁻¹). The followingmeasurements were used to calculate the ethylene content:

-   a) Height of the absorption band due to CH₂ group, with maximum at    5669 cm⁻¹, omitting area beneath a baseline drawn between the    6000-5500 cm⁻¹.-   b) Height of the shoulder at 5891 cm⁻¹ due to CH₃ group, omitting    area beneath a baseline drawn between the 6000-5500 cm⁻¹.

The ratio D5891/D5669 was calibrated by analyzing copolymers of knowncompositions, determined by NMR spectroscopy.

The following measurements were used to calculate the propylene content:

-   a) Area (ANIR) of the combination absorption bands between 4482 and    3950 cm⁻¹ which was used for spectrometric normalization of film    thickness.-   b) Area (A971) of the absorption band due to propylene sequences in    the range 986-952 cm⁻¹, omitting area beneath a baseline drawn    between the endpoints.

The ratio A971/ANIR was calibrated by analyzing copolymers of knowncompositions, determined by NMR spectroscopy.

Tg Determination Via DMTA (Dynamic Mechanical Thermal Analysis)

Molded specimen of 20 mm×5 mm×1 mm were fixed to the DMTA machine fortensile stress. The frequency of the sinusoidal oscillation was fixed at1 Hz. The DMTA translate the elastic response of the specimen startingfrom −100° C. (glassy state) to 130° C. (softening point). In this wayit was possible to plot the elastic response versus temperature. Theelastic modulus in DMTA for a viscoelastic material was defined as theratio between stress and strain also defined as complex modulusE*=E′+iE″. The DMTA can split the two components E′ and E″ by theirresonance and it was possible to plot E′ (elastic component), E″ (lossmodulus) and E″/E′=tan δ (damping factor) vs temperature. The glasstransition temperature Tg was assumed to be the temperature at themaximum of the curve tan=(δ) E″/E′ vs temperature.

Flexural Modulus*: ISO 178, was measured 24 hours after molding.

Tensile strength at yield*: ISO 527, was measured 24 hours aftermolding.

Tensile strength at break*: ISO 527, was measured 24 hours aftermolding.

Elongation at break and at yield*: ISO 527, was measured 24 hours aftermolding.

Notched IZOD impact test*: ISO 180/1A

The IZOD values were measured at 23° C., −20° C. and −30° C., 24 hoursafter molding.

Note: *Test specimens were prepared by injection molding according toISO 1873-2: 1989.

Gloss at 60°

A ISO D1 plaque of 1 mm was molded in an injection molding machine “NB60” (where 60 stands for 60 tons of clamping force) in accordance withthe following parameters.

-   -   Melt temperature=260° C.,    -   Mold temperature=40° C.,    -   Injection speed=100 mm/sec,    -   Holding time=10 sec,    -   Screw rotation=120 rpm

Injection and Holding pressures were properly set-up in order to assurea complete filling of the mold thus avoiding flashes.

Alternatively an injection molding machine “NB VE70” (where 70 standsfor 70 tons of clamping force) could have been used.

Gloss @ 60° is measured on the plaque according to ASTM D 2457.

Longitudinal and transversal thermal shrinkage

A plaque of 100×200×2.5 mm was molded in an injection molding machine

“SANDRETTO serie 7 190” (where 190 stands for 190 tons of clampingforce).

The injection conditions were:

-   -   melt temperature=250° C.;    -   mold temperature=40° C.;    -   injection time=8 seconds;    -   holding time=22 seconds;    -   screw diameter=55 mm.

The plaque was measured 24 hours after molding, through callipers, andthe shrinkage was given by:

${{Longitudinal}\mspace{14mu} {shrinkage}} = {\frac{200 - {read\_ value}}{200} \times 100}$${{Transversal}\mspace{14mu} {shrinkage}} = {\frac{100 - {read\_ value}}{100} \times 100}$

wherein 200 was the length (in mm) of the plaque along the flowdirection, measured immediately after molding;

100 was the length (in mm) of the plaque crosswise the flow direction,measured immediately after molding;

the read_value was the plaque length in the relevant direction.

EXAMPLES

The practice and advantages of the various embodiments, compositions andmethods as provided herein are disclosed below in the followingexamples. These Examples are illustrative, and are not intended to limitthe scope of the present disclosure, or appended claims, in any mannerwhatsoever.

Example 1

Preparation of the Ethylene Polymer Composition

The solid catalyst component used in polymerization was a Ziegler-Nattacatalyst component supported on magnesium chloride, containing titaniumand diisobutylphthalate as internal donor, prepared as follows.

An initial amount of microspheroidal MgCl₂.2.8C₂H₅OH was preparedaccording to the method described in Example 2 of U.S. Pat. No.4,399,054 but operating at 3,000 rpm instead of 10,000. The methoddescribed in Example 2 of U.S. Pat. No. 4,399,054 is hereby incorporatedby reference in full. The so obtained adduct was then subject to thermaldealcoholation at increasing temperatures from 30 to 130° C. operatingin nitrogen current until the molar alcohol content per mol of Mg was1.16.

Into a 1000 mL four-necked round flask, purged with nitrogen, 500 mL ofTiCl₄ was introduced at 0° C. While stirring, 30 grams of themicrospheroidal MgCl₂.1.16C₂H₅OH adduct (prepared as described above)were added. The temperature was raised to 120° C. and kept at this valuefor 60 minutes. During the temperature increase, an amount ofdiisobutylphthalate was added such as to have a Mg/diisobutylphthalatemolar ratio of 18. After the mentioned 60 minutes, the stirring wasstopped, the liquid was siphoned off and the treatment with TiCl₄ wasrepeated at 100° C. for 1 hour in the presence of an amount ofdiisobutylphthalate such as to have a Mg/diisobutylphthalate molar ratioof 27. After that time the stirring was stopped, the liquid was siphonedoff and the treatment with TiCl₄ was repeated at 100° C. for 30 min.After sedimentation and siphoning at 85° C. the solid was washed sixtimes with anhydrous hexane (6×100 ml) at 60° C.

Catalyst System and Prepolymerization Treatment

Before introducing it into the polymerization reactors, the solidcatalyst component described above was contacted at 30° C. for 9 minuteswith aluminum triethyl (TEAL) and dicyclopentyldimethoxysilane (DCPMS),in a TEAL/DCPMS weight ratio equal to about 15 and in such quantity thatthe TEAL/solid catalyst component weight ratio be equal to 4.

The catalyst system was then subjected to prepolymerization bymaintaining it in suspension in liquid propylene at 50° C. for about 75minutes before introducing it into the first polymerization reactor.

Polymerization

The polymerization was carried out in continuous in a series of twogas-phase reactors equipped with devices to transfer the product fromthe first reactor to the second one.

Into the first gas phase polymerization reactor an ethylene/propylenecopolymer (component A)) was produced by feeding in a continuous andconstant flow the prepolymerized catalyst system, hydrogen (used asmolecular weight regulator), ethylene and propylene in the gas state.

The ethylene polymer coming from the first reactor was discharged in acontinuous flow and, after having been purged of unreacted monomers, wasintroduced, in a continuous flow, into the second gas phase reactor,together with quantitatively constant flows of hydrogen, ethylene andpropylene in the gas state.

In the second reactor a second ethylene/propylene copolymer (componentB)) was produced. Polymerization conditions, molar ratio of thereactants and composition of the copolymers obtained are shown in TableI.

The polymer particles exiting the second reactor, which constitute thenot stabilized ethylene polymer composition according to the presentdisclosure, were subjected to a steam treatment to remove the reactivemonomers and volatile substances, and then dried.

Then the polymer particles were mixed with a usual stabilizing additivecomposition in a twin screw extruder Berstorff ZE 25 (length/diameterratio of screws: 33) and extruded under nitrogen atmosphere under thefollowing conditions:

-   Rotation speed: 250 rpm;-   Extruder output: 15 kg/hour;-   Melt temperature: 280-290° C.

The stabilizing additive composition was made of the followingcomponents:

-   0.1% by weight of Irganox® 1010;-   0.1% by weight of Irgafos® 168;-   0.04% by weight of DHT-4A (hydrotalcite).

Irganox® 1010 is2,2-bis[3-[,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl)-1-oxopropoxy]methyl]-1,3-propanediyl-3,5-bis(1,1-dimethylethyl)-4-hydroxybenzene-propanoate,while Irgafos® 168 is tris(2,4-di-tert.-butylphenyl)phosphite.

The percent amounts referred to the total weight of the polymer andstabilizing additive composition.

The characteristics relating to the polymer composition, reported inTable II, were obtained from measurements carried out on the so extrudedpolymer, which constitutes the stabilized ethylene polymer compositionaccording to the exemplary embodiments disclosed herein.

Preparation of a Blend of the Stabilized Ethylene Polymer Compositionwith Propylene Polymer:

The stabilized ethylene polymer composition prepared as described above(hereinafter called SEP) was blended by extrusion under the previouslydescribed conditions with a heterophasic polypropylene composition (HPP)and the other additives hereinafter described, in the proportionsreported below and in Table III. The properties of the so obtained finalcomposition are reported in Table III.

Added components

-   1 HPP: heterophasic polypropylene composition having MFR of 16.5    g/10 min., made of 70% by weight of propylene homopolymer with    isotactic index of 98% (fraction insoluble in xylene at 25° C.,    determined as described above) and 30% by weight of an    ethylene/propylene copolymer containing 49% by weight of ethylene;-   2 talc HTP Ultra 5C: fine talc powder comprising about 98% by weight    of particles having particle size of less than 5 μm;-   3 carbon black master-batch having total MFR of about 0.6 g/10 min.    (measured according to ISO 1133 at 230° C./5 kg load) and made of    40% by weight of carbon black and 60% of a copolymer of propylene    with 8% by weight of ethylene, having MFR of about 45 g/10 min.;-   4 Irganox® B 215 (made of about 34% by weight of Irganox® 1010 and    66% of Irgafos® 168);

The added amounts of components 1 to 4 are the following (percent byweight with respect to the total weight):

Component Amount 1 51.5%  2  12% 3 1.3% 4 0.2%

Comparative Example 1C

A comparative polyethylene composition was prepared with the samecatalyst and polymerization process as in Example 1 and was thenextruded with the same stabilizing additive composition and with thesame extrusion conditions as in Example 1. The specific polymerizationconditions and the resulting polymer properties are reported in Table Iand Table II.

The stabilized composition was used in the preparation of a blend withthe same added components in the same amounts as in Example 1.

The properties of the so obtained final composition are reported inTable III.

TABLE I Example No. 1 1C 1^(st) Reactor (component A)) Temperature ° C.70 70 Pressure barg 20 20 H2/C2− mol. 0.59 0.37 C3−/(C3− + C2−) mol.0.15 0.12 Split wt % 40 40 Xylene soluble (XS_(A)) wt % 2.4 4.3 MFR ofA) g/10 min. 5.7 14 Density of A) g/cm³ 0.943 0.940 C3− content of A) wt% 3.2 2.8 2^(nd) Reactor (component B)) Temperature ° C. 65 65 Pressurebarg 20 20 H2/C2− mol. 0.10 0.13 C2−/(C2− + C3−) mol. 0.41 0.68 Split wt% 60 60 C2− content of B) wt % 60 80 Xylene soluble of B) (XS_(B)) wt %73 36 Intrinsic Viscosity of XS_(B) dl/g 2.2 2.3 Tg of A) + B) ° C. −45−46 Notes: C3− = propylene; C2− = ethylene; split = amount of polymerproduced in the concerned reactor.

TABLE II Example No. 1 1C ΔHfus J/g 78.8 100.1 Tm ° C. 125 123.9 MFRg/10 min. 1.15 0.56 Xylene soluble (XS_(TOT)) wt % 44.5 23.1 IntrinsicViscosity of XS_(TOT) dl/g 2.17 2.6 C2− content of XS_(TOT) wt % 53 70Total C2− content wt % 73.6* 84.9 Total C3− content wt % 26.4 15.1*Flexural Modulus MPa 120 260 Notes: C3− = propylene; C2− = ethylene;*Calculated values.

TABLE III Example No. 1 1C SEP of EXAMPLE 1 1C SEP amount wt % 35 35 MFRg/10 min. 5.3 4.2 Flexural Modulus MPa 810 960 Tensile Strength at YieldMPa 12.2 14.6 Elongation at Yield % 14.0 12.8 Tensile strength at breakMPa 12.7 16.9 Elongation at break % 570 460 Gloss at 60° ‰ 57 29Longitudinal shrinkage % 0.29 0.4 Transversal shrinkage % 0.52 0.63 IZODImpact Str. at 23° C. KJ/m² 61.7 64.7 IZOD Impact Str. at −20° KJ/m²73.2 58.6 IZOD Impact Str. at −30° KJ/m² 67.7 35.7

What is claimed is:
 1. An ethylene polymer composition having a fusion enthalpy ΔH_(fus), measured by Differential Scanning calorimetry with a heating rate of 20° C. per minute, of 60 J/g or more, preferably of 70 J/g or more, and comprising, all percent amounts being by weight: A) 25-55%, preferably 30-45%, of an ethylene polymer containing 10% or less referred to the weight of A), of a fraction XS_(A) soluble in xylene at 25° C.; B) 45-75%, preferably 55-70%, of a copolymer of ethylene and propylene containing from 45% to 70% of ethylene and 60% or more of a fraction XS_(B) soluble in xylene at 25° C., both the ethylene of the copolymer and XS_(B) amounts being referred to the weight of B); wherein the amounts of A) and B) are referred to the total weight of A)+B).
 2. The ethylene polymer composition of claim 1, wherein the ethylene polymer A) is an ethylene homopolymer (i) or a copolymer (ii) of ethylene with one or more comonomers selected from olefins having formula CH₂═CHR wherein R is an alkyl radical, linear or branched, having from 1 to 10 carbon atoms, or a mixture of (i) and (ii).
 3. The ethylene polymer composition of claim 1, wherein the ethylene polymer A) has a density of from 0.930 to 0.960 g/cm³, determined according to ISO 1183 at 23° C.
 4. The ethylene polymer composition of claim 1, showing a melting peak at a temperature Tm of 120° C. or higher, measured by Differential Scanning calorimetry with a heating rate of 20° C. per minute.
 5. The ethylene polymer composition of claim 1, wherein the intrinsic viscosity [η] of the XS_(B) fraction is of 2 dl/g or more.
 6. The ethylene polymer composition of claim 1, having a MFR value of from 0.3 to 5 g/10 min, determined according to ISO 1133 at 230° C. with a load of 2.16 kg.
 7. The ethylene polymer composition of claim 1, having at least one of the following additional features: a MFR value of the ethylene polymer A), determined according to ISO 1133 at 230° C. with a load of 2.16 kg, of from 1 to 15 g/10 min.; glass transition temperature (Tg), measured on the blend of A)+B), of equal to or higher than −50° C.; Tg of component B) of equal to or higher than −50° C.; an ethylene content, determined on the total amount of A)+B), of 65%-85% by weight; an amount of total fraction XS_(TOT) soluble in xylene at 25° C., determined by extraction carried out on the total amount of A)+B), of 35%-60% by weight; an intrinsic viscosity [η] of the XS_(TOT) fraction of 1.8 dl/g or more; an ethylene content of the the XS_(TOT) fraction of 45%-60% by weight; a flexural modulus value from 90 to 200 MPa.
 8. Polymerization process for preparing the ethylene polymer composition of claim 1, comprising at least two sequential stages, wherein components A) and B) are prepared in separate subsequent stages, operating in each stage, except the first stage, in the presence of the polymer formed and the catalyst used in the preceding stage.
 9. A polyolefin composition comprising the ethylene polymer composition of claim 1 and at least 50% by weight, referred to the total weight of the polyolefin composition, of one or more additional polyolefins.
 10. The polyolefin composition of claim 9, wherein the additional polyolefin or polyolefins are selected from propylene homoploymers and copolymers.
 11. Formed articles comprising the polyolefin composition of claim
 9. 12. Formed articles according to claim 11, comprising injection molded articles.
 13. Formed articles comprising the polyolefin composition of claim
 10. 14. Formed articles according to claim 13, comprising injection molded articles. 